Pyrex7740 glass (a kind of glass that contains alkali ions, wherein Pyrex is a product brand of Corning Inc.) has a thermal expansion coefficient close to that of silicon material, high light transmittance and high strength, and can form a high-strength bonding connection with Si substrate through an anodic bonding process; in that way, on the bonding surface robust Si—O covalent bonds are formed, the strength of which is even higher than that of the Si material itself. With such features, Pyrex7740 glass is widely applied in MEMS encapsulation, microfluid and MOEMS (Micro-Optical-Electromechanical System) fields, etc. Glass micro-cavity structure has important applications in production and encapsulation of MEMS elements and production of microfluidics elements. However, micro-machining of glass is extremely difficult. At present, there are several machining processes available, such as sand blasting, ECDM, wet etching, dry etching, and laser drilling. Glass machined through the above machining processes usually has a high surface roughness; in addition, the above machining processes usually have a low machining speed and a high process cost.
Another machining process is negative pressure thermoforming process. The negative pressure molding process disclosed in Chinese Patent Application No. 200710190226.2 comprises the following steps: etching an Si trench on silicon; bonding glass to the silicon by anodic bonding in a vacuum; heating them in the air to a high temperature and forcing the glass into the silicon cavity under negative pressure between the exterior and interior of the cavity, so as to form glass micro-cavity structures on the back. Since micro flow channels are formed on the back of the glass wafer in the negative pressure molding process, the height of the micro-cavities formed on the back is small (not greater than the thickness of the glass wafer) when the glass wafer is thicker. To obtain glass micro-cavities with a high height, the silicon mold must have cavities with a high depth-width ratio, so as to provide more space for glass deformation.
Another process is a self-inflation process. This process comprises the following steps: bonding glass with silicon under one bar, and utilizing sealed gas as the driving force to accomplish thermoforming of the glass. Since the process requires enough gas to provide enough driving force for self-inflation and thereby form higher glass micro-cavities, unusually deep pores with high depth-width ratio have to be etched on the silicon, and sometimes even a non-standard thicken silicon wafer is required (sometimes, the required thickness is 900 μm or above; see Glass Blowing on a Wafer Level, JOURNAL OF MICROELECTROMECHANICAL SYSTEMS, VOL. 16, NO. 2, APRIL 2007); as a result, the process time will be increased significantly, the cost of the dry etching process will be very high, the material cost will be increased significantly, and thereby the total cost will be increased. To provide a further driving force for molding so as to form spherical glass micro-cavities with a higher height, another piece of silicon wafer with pore structures has to be bonded; consequently, the cost will be increased, and the additional bonding process may cause silicon wafer wrap and thereby decrease the rate of finished products. Another drawback of the above process is: if a complex microfluid system is to be formed, large-area dry etching is required, which will cause higher cost; in addition, when flow channels and cavities in different sizes are molded, it is difficult to form cavities with different heights on a silicon wafer through dry etching, thus the gas supply is insufficient when molding complex glass structure.